Crosslinkabel dispersion powders as binders for fibers

ABSTRACT

PCT No. PCT/EP94/00625 Sec. 371 Date Aug. 29, 1995 Sec. 102(e) Date Aug. 29, 1995 PCT Filed Mar. 3, 1994 PCT Pub. No. WO94/20661 PCT Pub. Date Sep. 15, 1994This invention covers the use of cross-linkable redispersible dispersion powders based on vinyl ester copolymers or (meth)acrylic acid ester copolymers as binders for the dry binding of fibre materials.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The invention relates to the use of crosslinkable, redispersibledispersion powders based on vinyl ester copolymers or (meth)acrylic acidester copolymers as binders for dry binding of fibre materials.

To increase resistance to mechanical stress, fibre structures arecompacted with binders. These binders can be used in the form of solids,such as powders, granules or fibres, or as liquids, such as solutions ordispersions. The increased strength results from binding of the fibresby the polymers, which adhere to the fibre and in this way reinforce thefibre structures.

2) Background Art

A procedure is known from WO-A 90/14457 in which, after a carding step,glass fibres are mixed with a thermoplastic powder, for examplepolypropylene, polyester or polyamide, and the fibre structure is thencompacted at elevated temperature and under pressure. AU-B 36659/89 alsodescribes the compaction of glass fibre materials by means ofthermoplastic powders. The use of polyesters or polystyrene isrecommended here. A disadvantage is the low strength of the fibrestructures thus bonded in contact with water or solvents.

If fibre non-wovens of increased strength, above all in contact withwater or solvents or at elevated temperature, are to be obtained,polymers which can crosslink or polymerize completely in a particularprocessing step are employed. EP-B 0080144 (U.S. Pat. No. 4,451,315)describes the compaction of fibre non-wovens of polyester, polyamide orcotton fibres with emulsions of self-crosslinking acrylic estercopolymers, ethylene/vinyl acetate copolymers or self-crosslinkingsynthetic rubbers. Non-woven materials of high strength are indeedobtained by this process; the disadvantage of using aqueous binders,nevertheless, is the high drying expenditure; furthermore, distributionof the binder in the fibre matrix is problematic.

The compaction of pulverulent, crosslinkable polymers based onphenol-formaldehyde resins is described in U.S. Pat. No. 4,612,224. Thedisadvantage of this binder system is the high formaldehyde emissionduring preparation and use of the fibre materials thus compacted.

The invention was based on the object of providing binders forcompaction of fibre materials which can be employed as powders and havea high wet strength and good heat stability, avoiding harmful emissionsduring processing.

The object has been achieved by the development of a dry binder based onthermoplastic copolymers which have only small contents of comonomerswhich have a crosslinking action and nevertheless effect a high strengthcoupled with a negligible formaldehyde emission.

Thermosetting copolymers based on acrylic acid esters and/or vinylesters, which also comprise (meth)acrylic acid esters of mono- orpolyfunctional hydroxycarboxylic acids and N-alkoxyalkyl(meth)acrylamideas crosslinking components, are described as pulverulent paints in DE-A2701490 (U.S. Pat. No. 4,129,545).

SUMMARY OF THE INVENTION

The invention relates to the use of crosslinkable, redispersibledispersion powders based on vinyl ester copolymers or (meth)acrylic acidester copolymers as binders for dry binding of fibre materials, whereinthe vinyl ester copolymers comprise one or more monomers from the groupcomprising vinyl esters of unbranched or branched alkylcarboxylic acidshaving 1 to 15 C atoms, the (meth)acrylic acid ester copolymers compriseone or more monomers from the group comprising methacrylic acid estersand acrylic acid esters of alcohols having 1 to 10 C atoms and the vinylester and (meth)acrylic acid ester copolymers in each case comprise 0.1to 10% by weight, based on the total weight of the copolymer, of one ormore ethylenically unsaturated comonomers having a crosslinking action.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred vinyl esters are vinyl acetate, vinyl propionate, vinylbutyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate,vinyl pivalate and vinyl esters of branched monocarboxylic acids having9 to 10 C atoms, for example VeoVa9® or VeoVa10®. Vinyl acetate isparticularly preferred.

Preferred methacrylic acid esters or acrylic acid esters are methylacrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate,propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butylmethacrylate and 2-ethylhexol acrylate. Methyl acrylate, methylmethacrylate, n-butyl acrylate and 2-ethylhexyl acrylate areparticularly preferred.

Preferred ethylenically unsaturated comonomers having a crosslinkingaction are, for example, acrylamidoglycolic acid (AGA),methacrylamidoglycolate acid methyl ester (MAGME), N-methylolacrylamide(NMAA), N-methylolmethacrylamide, allyl N-methylolcarbamate, alkylethers, such as isobutyl [sic] ether, or esters of N-methylolacrylamide,of N-methylolmethacrylamide or of allyl N-methylolcarbamate.N-methylolacrylamide (NMAA) and N-methylolmethacrylamide areparticularly preferred.

If appropriate, the vinyl ester copolymers can comprise 1.0 to 65% byweight, based on the total weight of the comonomer phase, of α-olefins,such as ethylene or propylene, and/or vinyl aromatics, such as styrene,and/or vinyl halides, such as vinyl chloride, and/or acrylic acid estersor methacrylic acid esters of alcohols having 1 to 10 C atoms, such asmethyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate,n-butyl methacrylate or 2-ethylhexyl acrylate, and/or ethylenicallyunsaturated dicarboxylic acid esters or derivatives thereof, such asdiisopropyl fumarate, the dimethyl, dibutyl and diethyl esters of maleicacid or fumaric acid or maleic anhydride. The choice of the monomersmentioned is made here such that copolymers having a glass transitiontemperature T_(g) of -20° C. to 60° C. are obtained.

If appropriate, the (meth)acrylic acid ester copolymers can comprise 1.0to 65% by weight, based on the total weight of the comonomer phase, ofα-olefins, such as ethylene or propylene, and/or vinyl aromatics, suchas styrene, and/or vinyl halides, such as vinyl chloride, and/orethylenically unsaturated dicarboxylic acid esters or derivativesthereof, such as diisopropyl fumarate, the dimethyl, dibutyl and diethylesters of maleic acid or fumaric acid or maleic anhydride. The choice ofthe monomers mentioned is made here such that copolymers having a glasstransition temperature T_(g) of -20° C. to +60° C. are obtained.

In a preferred embodiment, the vinyl ester copolymers and the(meth)acrylic acid ester copolymers also comprise 0.05 to 3.0% byweight, based on the total weight of the comonomer mixture, of auxiliarymonomers from the group comprising ethylenically unsaturated carboxylicacids, preferably acrylic acid or methacrylic acid, from the groupcomprising ethylenically unsaturated carboxylic acid amides, preferablyacrylamide, from the group comprising ethylenically unsaturatedsulphonic acids and salts thereof, preferably vinylsulphonic acid,and/or from the group comprising polyethylenically unsaturatedcomonomers, for example divinyl adipate, diallyl maleate, allylmethacrylate or triallyl cyanurate. Copolymers which comprise acrylamidein an equimolar amount to the particular crosslinking system areparticularly preferred.

Preferred vinyl ester copolymers comprise:

70 to 95% by weight of vinyl ester, in particular vinyl acetate, as wellas 5 to 25% by weight of α-olefin, in particular ethylene, and/or 5 to30% by weight of diisopropyl fumarate and 0.1 to 10.0% by weight ofN-methylol(meth)acrylamide, or

50 to 70% by weight of vinyl ester, in particular vinyl acetate, 10 to30% by weight of vinyl ester of an α-branched carboxylic acid, inparticular VeoVa9® and/or VeoVa10®, 5 to 25% by weight of ethylene and0.1 to 10.0% by weight of N-methylol(meth)acrylamide, or

15 to 50% by weight of vinyl ester, in particular vinyl acetate, 30 to65% by weight of vinyl chloride and/or diisopropyl fumarate, 5 to 25% byweight of ethylene and 0.1 to 10% by weight ofN-methylol(meth)acrylamide, or

50 to 70% by weight of vinyl ester, in particular vinyl acetate, 1 to30% by weight of acrylic acid ester, in particular n-butyl acrylate or2-ethylhexyl acrylate, 5 to 25% by weight of ethylene and 0.1 to 10.0%by weight of N-methylol(meth)acrylamide. The data in % by weight in eachcase add up to 100% by weight.

Preferred (meth)acrylic acid ester copolymers comprises

30 to 70% by weight of methyl methacrylate, 70 to 30% by weight ofn-butyl acrylate and/or 2-ethylhexyl acrylate and 0.1 to 10% by weightof N-methylol(meth)acrylamide, or

30 to 70% by weight of styrene and 70 to 30% by weight of n-butylacrylate and/or 2-ethylhexyl acrylate and 0.1 to 10% by weight ofN-methylol(meth)acrylamide. The data in % by weight in each case add upto 100% by weight.

The vinyl ester copolymers and the (meth)acrylic acid ester copolymersare preferably prepared by the emulsion polymerization process. Thepolymerization can be carried out discontinuously or continuously, withor without the use of seed latices, by initially introducing all of theconstituents or individual constituents of the reaction mixture into thereaction vessel, or by initially introducing portions of theconstituents or of individual constituents of the reaction mixture intothe reaction vessel and subsequently metering in the remainder, or bythe metering process without initial introduction of constituents. Allthe meterings are preferably carried out at the rate at which theparticular component is consumed.

The polymerization is carried out in a temperature range from 0° to 100°C. and is initiated by the methods usually employed for emulsionpolymerization. The initiation is carried out by means of the customarywater-soluble agents which form free radicals, which are preferablyemployed in amounts of 0.01 to 3.0% by weight, based on the total weightof the monomers. Examples of these are ammonium and potassiumpersulphate and peroxodisulphate; hydrogen peroxide; alkylhydroperoxides, such as tert-butyl hydroperoxide; potassium, sodium andammonium peroxodiphosphate; and azo compounds, such asazobisisobutyronitrile or azobiscyanovaleric acid. If appropriate, thefree radical initiators mentioned can also be combined in a known mannerwith 0.01 to 0.5% by weight, based on the total weight of the monomers,of reducing agents. Formaldehyde-sulphoxylate salts or ascorbic acid,for example, are suitable. In the case of redox initiation, one or bothredox catalyst components are preferably metered in during the reaction.

Dispersing agents which can be employed are all the emulsifiers andprotective colloids usually used during emulsion polymerization. 1 to 6%by weight, based on the total weight of monomers, of emulsifier ispreferably employed. Suitable agents are, for example, anionicsurfactants, such as alkyl sulphates having a chain length of 8 to 18 Catoms, alkyl and alkylaryl ether sulphates having 8 to 18 C atoms in thehydrophobic radical and up to 40 ethylene oxide or propylene oxideunits, alkyl- or alkylarylsulphonates having 8 to 18 C atoms and estersand half-esters of sulphosuccinic acid with monohydric alcohols oralkylphenols. Suitable nonionic surfactants are, for example, alkylpolyglycol ethers or alkylaryl polyglycol ethers having 8 to 40 ethyleneoxide units.

If appropriate, protective colloids can be employed, preferably inamounts of up to 15% by weight, based on the total weight of themonomers. Examples of these are vinyl alcohol/vinyl acetate copolymerscontaining 80 to 100 mol % of vinyl alcohol units, polyvinylpyrrolidoneshaving a molecular weight of 5000 to 400,000 and hydroxyethylcelluloseshaving a degree of substitution range of 1.5 to 3.

The pH range desired for the polymerization, which is in general between2.5 and 10, preferably 3 and 8, can be established in a known manner byacids, bases or customary buffer salts, such as alkali metal phosphatesor alkali metal carbonates. To establish the molecular weight, theregulators usually used, for example mercaptans, aldehydes andchlorinated hydrocarbons, can be added during the polymerization.

To prepare the dispersion powders, the dispersion is dried, preferablyspray-dried or freeze-dried, particularly preferably spray-dried. Theknown devices can be resorted to here, such as, for example, sprayingthrough multi-component nozzles or using a disc, in a stream of dry gaswhich is heated if appropriate. In general, temperatures above 250° C.are not used. The optimum temperature of the dry gas can be determinedin a few experiments; temperatures above 60° C. have often proved to beparticularly suitable.

To increase storage stability and in order to prevent caking andblocking, for example in the case of powders of low glass transitiontemperature T_(g), an antiblocking agent, for example aluminiumsilicates, kieselguhr or calcium carbonate, is added, if appropriate,during drying. Furthermore, defoamers, for example based on silicones orhydrocarbons, or atomization aids, for example polyvinyl alcohols orwater-soluble melamineformaldehyde condensation products, can also beadded to the dispersion if appropriate.

In a preferred embodiment, the dispersion powders also comprise 0 to 30%by weight, particularly preferably 1 to 15% by weight, based on the basepolymer, of polyvinyl alcohol having a degree of hydrolysis of 85 to 94mol %, and/or 0 to 10% by weight of vinyl alcohol copolymers having 5 to35% by weight of 1-methylvinyl alcohol units, and/or 0 to 304 by weight,particularly preferably 4 to 20% by weight, based on the total weight ofpolymeric constituents, of antiblocking agent, and if appropriate up to2% by weight, based on the base polymer, of defoamer.

The crosslinkable dispersion powder is suitable for compaction ofnaturally occurring or synthetic fibre materials. Examples of these arewood fibres, cellulose fibres, wool, cotton, mineral fibres, ceramicfibres, synthetic fibres based on fibre-forming polymers, such asviscose fibres, fibres of polyethylene, polypropylene, polyester,polyamide, polyacrylonitrile or carbon, fibres of homo- or copolymers ofvinyl chloride or fibres of homo- or copolymers of tetrafluoroethylene.

Before the compaction, the fibres are spread out in a sheet-like manner.The processes for this are known and depend primarily on the use towhich the compacted fibre material is put. The fibres can be laid out bymeans of an air laying, wet laying, direct spinning or carding device.If approcriate, the sheet-like structures can also be compactedmechanically, for example by cross-laying, needling or water jetcompaction, before compaction with the binder.

In the use according to the invention, the pulverulent binder issprinkled onto, sprinkled into (for example in the case of cardedwadding) or shaken into the optionally mechanically precompacted fibrematerial or mixed directly with the fibre in a manner which is known perse. The amount of binder needed for compaction of the fibre material isbetween 5 and 50% by weight of binder, based on the fibre weight,depending on the field of use.

In a preferred embodiment, the sheet-like fibre structures are moistenedwith water before the binder is sprinkled on. The amount of water neededfor this is, in general, 5 to 60% by weight, preferably 10 to 35% byweight, in each case based on the total weight of dry mixture of fibreand binder. In this procedure, binding of the fibre material can beinitiated by application of pressure and temperature after the binderhas been sprinkled on.

However, it is also possible for the water to be removed at atemperature of 80° to 110° C., for example by heating the fibrestructure in a stream of air, after the binder has been sprinkled ontothe moist fibre. In this case, before crosslinking of the binder, watermust be sprayed onto the fibre again in the stated amount. Pre-bindingof the fibre material is achieved by this procedure, which means thatthe fibre material can be transported in a pre-bound but not crosslinkedform. This is an essential advantage over binding with dispersions, inwhich this pre-binding is not possible since it can no longer bereactivated.

For production of shaped articles from a mixture of fibre material andbinder powder in the stated amounts, a procedure is preferably followedin which the fibre and binder are mixed in the dry state, and water isfirst added to the mixture in the stated amount before the pressure andheat treatment.

Compaction of the fibre material, whether as a sheet-like structure oras a fibre/binder mixture for production of shaped articles, is carriedout by heating at a temperature of preferably 100° to 200° C. under apressure of up to 100 bar. The pressure and temperature ranges to beapplied depend primarily on the nature of the fibre material.

A preferred use is the production of mouldings from fibre materialswhich are compacted with the cross-linkable powder. For this, the fibresare mixed with the binder in the stated amounts and, after addition ofwater, the mixtures are compacted under the action of pressure andtemperature in the stated ranges. Examples of this use are theproduction of soundproofing mats and mouldings for the car industry.Phenolic resins have hitherto been employed above all as binders formouldings. The associated disadvantages of emission of formaldehyde andphenol do not occur with the use according to the invention.

Use for binding glass fibres is also preferred.

Another preferred use is that for binding wadding, for example for theproduction of upholstery, insulating and filter wadding. Fusible fibres,fusible powders and dispersions of vinyl chloride polymers, for thepurpose of flameproofing, have primarily been employed for this purposeto date. Compared with the use of fusible fibres or fusible powders, theuse according to the invention is distinguished by the fact that thedesired strength can even be achieved with lower application amounts.Another advantage of the use according to the invention of crosslinkabledispersion powders is that admixing of pulverulent additives, forexample flameproofing agents, pigments and salts, is not so severelylimited in comparison with aqueous dispersions, both in respect of thenature of the additive and in respect of their physicochemicalproperties. The dispersion powders are miscible with pulverulentadditives in any desired amount, without adding surfactants and withoutlimiting the pot lives.

Similar advantages are offered by the similarly preferred use of thecrosslinkable dispersion powders for the production of non-wovenmaterials from fibres, in which polymer dispersions, fusible powders andfusible fibres likewise have been employed to date.

The use of the crosslinkable powders for the production of needle feltis also preferred. In the prior art, aqueous dispersions based onstyrene/butadiene rubber, ethylene/vinyl acetate and ethylene/vinylacetate/vinyl chloride copolymers are employed above all for thispurpose. The dispersions are applied to the fibre fabric, which has beencompacted by needling, and converted into a film in a hot calender. Inthe use according to the invention of the crosslinkable polymer powders,even taking into account the amount of water added for crosslinking, thedrier capacity to be expended, and therefore the energy requirementneeded for production, are reduced considerably.

Summarizing, the advantage of the use of the crosslinkable dispersionpowders in applications where aqueous systems are traditionallyemployed, for example in the binding of non-woven material, lies in asignificant reduction in drying expenditure and in the amounts of wastewater. In applications where prepolymers or oligomers which can bepolymerized completely (for example phenolic resins) are traditionallyemployed, which are, for example, the binding of glass fibres andproduction of mouldings from fibre materials, the advantage lies in asignificant reduction in the reaction temperatures and in asimplification of the composition of the reaction mixture.

The following examples serve to further illustrate the invention:

EXAMPLE 1

(non-woven compaction):

Non-wovens of a polyester fibre (6.7 dtex/60 mm) with a weight per unitarea of about 50 g/m² were produced in a laboratory carder. Directly atthe carder exit, 20% by weight of water, based on the total weight offibre and binder, and then a dispersion powder based on a vinyl acetatepolymer with 1% by weight of N-methylolacrylamide in the amounts statedbelow were sprinkled in. The non-wovens were compacted at thetemperatures stated below. The mechanical properties (breaking force andelongation) in the dry and wet (after storage in water for 1 minute)state were determined in accordance with DIN 53857.

Non-woven 1: application of 26.2% by weight, drier temperature 100° C.

Non-woven 2: application of 28.4% by weight, drier temperature 150° C.

Non-woven 3: application of 27.6% by weight, drier temperature 180° C.

                  TABLE 1                                                         ______________________________________                                                  Breaking                                                                      force        Elongation                                                                             Relative BF                                   Non-woven BF [N]       [%]      [%]                                           ______________________________________                                        1      dry    4.8          46                                                        wet    0.4          37     8.3                                         2      dry    4.4          54                                                        wet    0.9          41     20.5                                        3      dry    5.8          42                                                        wet    2.2          33     37.9                                        ______________________________________                                         *Relative BF = BF.sub.wet × 100/BF.sub.dry                         

EXAMPLE 2

(fibre shaped article production):

For production of sheets, 80 g of reclaimed cotton were mixed with 20 gof dispersion powder of the composition stated below and the mixture waslaid out over an area of 20×20 cm². Some of the mixtures were alsomoistened with water by spray application. The mixtures were thenpressed under 50 bar for 5 minutes at temperatures of between 180° and200° C., so that sheets 2 mm thick and weighing 200 g/m² were formed.The breaking force in the dry and wet (after storage in water for 10minutes) state was determined in accordance with DIN 53857. To evaluateswelling, the sheets were stored in water at room temperature for 24hours.

Sheet 1: pressed without moisture, dispersion powder based on a vinylacetate homopolymer

Sheet 2: pressed with 20 g of water, dispersion powder based on a vinylacetate homopolymer

Sheet 3: pressed without moisture, dispersion powder based on a vinylacetate polymer with 1% by weight of N-methylolacrylamide

Sheet 4: pressed with 20 g of water, dispersion powder based on a vinylacetate polymer with 1% by weight of N-methylolacrylamide

                  TABLE 2                                                         ______________________________________                                                  Breaking force                                                                           Relative BF                                              Sheet     BF [N]     [%]          Swelling                                    ______________________________________                                        1     dry     297                                                                   wet     16         5.4        severe                                    2     dry     570                                                                   wet     163        28.6       slight                                    3     dry     822                                                                   wet     394        47.9       severe                                    4     dry     2251                                                                  wet     1279       56.8       none                                      ______________________________________                                    

What is claimed is:
 1. A process for binding fiber materials whichcomprises(a) contacting said materials with from 5 to 50% by weightbased on the weight of the fiber material, of a binder based on a vinylester copolymer dry powder or a (meth)acrylic acid ester copolymerpowder, said vinyl ester copolymer comprising at least one monomerselected from the group consisting of vinyl esters of unbranched orbranched alkyl carboxylic acids having 1 to 15 C atoms and the(meth)acrylic acid ester copolymer comprising at least one monomerselected from the group consisting of methacrylic acid esters ofalcohols having 1 to 10 carbon atoms and the vinyl ester and(meth)acrylic acid ester copolymer, in each case comprising 0.1 to 10%by weight, based on the total weight of the copolymer of at least oneethylenically unsaturated comonomer having a crosslinking action; (b)moistening the material with 5 to 60% by weight of water based on thetotal weight of dry mixture of fiber and binder before or after thebinder has been contacted with the fiber material, and (c) heating at100° to 200° C. under a pressure of up to 100 bar to bind the fibers. 2.The process of claim 1 wherein the fibre material is sprinkled on thematerial in the form of a crosslinkable redispersible dispersion powder.3. The process according to claim 2, wherein, after the dispersionpowder has been sprinkled onto the moist fibre, the water is removed byheating the fibre structure in a stream of air at a temperature of 80°to 110° C. and before the crosslinking, water is sprayed on the fibre.4. The process of claim 1 wherein the fibre material is in the form of asheet or shaped article and the binder is sprinkled on the material inthe form of a crosslinkable redispersible dispersion powder.
 5. Theprocess of claim 1 wherein the fibre material is a mechanicallycompacted fibre material and the binder is sprinkled on the material inthe form of a crosslinkable redispersible dispersion powder.
 6. Theprocess of claim 1 wherein the fibre material is glass fibres, wadding,a non-woven material or needle felt.